The tt̅ spi+n correlation at production is a fundamental
prediction of QCD and a potentially incisive test of new physics coupled
to top quarks. We measure the tt̅ spi+n state in pp̅ collisions at
√s=1.96 TeV using 1001 candidate events in the lepton plus jets
decay channel reconstructed in the CDF II detector. In the helicity basis,
for a top-quark mass of 172.5 GeV/c2, we find a spi+n correlation
coefficient κ=0.60±0.50 (stat)±0.16 (syst), consistent with
the QCD prediction, κ≈0.40.